tools/power/x86/intel-speed-select: Remove unused non_block flag

variable 'non_block' is always 0, thus remove the variable and the
handling for "non_block != 0" case.

Signed-off-by: Zhang Rui <rui.zhang@intel.com>
Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>